The field of art to which this invention pertains is water-soluble polymers.
Thickeners for aqueous fluids are used in a number of industrial and personal care applications. However, after the purpose for using the thickened aqueous fluid has been served, it is often desirable to lower the viscosity of the aqueous fluid. This lowering of viscosity is accomplished by using a "breaker" which acts on the water-soluble polymer to reduce its molecular weight and to thin the fluid in which it is dissolved.
The breaking of aqueous gels or thickened aqueous fluids has been accomplished by using a variety of techniques. One such method is by the degradative action of acids, enzymes, or mild oxidizing agents as disclosed in U.S. Pat. No. 4,169,791. In U.S. Pat. No. 4,464,268, sodium hypochlorite is described as being a drastic treating agent for degrading water-soluble polymers. The use of ammonium and alkali metal persulfates in combination with tertiary amines is disclosed in U.S. Pat. No. 4,250,044 as being suitable breaker systems for high viscosity fluids. Lithium hypochlorite is described as a breaker material in Oil and Gas Journal, Dec. 12, 1983, pp 96 to 101. The thickening of aqueous fluids and various techniques for reducing the viscosity of the fluids is described in such patents as U.S. Pat. Nos. 3,002,960, 3,779,914, 4,144,179 and 4,552,668. As described in U.S. Pat. No. 4,654,043, starch sizing agents are degraded by treatment with hypochlorites and amino compounds.
In commonly assigned U.S. Pat. No. 4,647,385, the viscosity of thickened aqueous solutions is reduced by the addition of alkali metal and alkaline earth metal salts of hypochlorous acid plus tertiary amines to the solutions. The combination of the salt and the tertiary amine is much more efficient in speed of reduction in viscosity and in the completeness of the degradation of the polymer in the solution than the use of the metal salt alone.
Thickened aqueous fluids are useful in oil recovery processes, particularly in the practice of fracturing subterranean formations. In the fracturing operations, a thickened fluid having granular insoluble particulate material suspended therein, is injected down a well penetrating the formation under hydraulic pressure. The pressurized fluid causes the formation to crack or fracture. The suspended insoluble granular particles are forced into the fractures and prop open the fractures when the fracturing pressures are released. Before the well is put back into operation, the thickened fluid must be removed from the well. Such removal is facilitated if the viscosity can be quickly reduced.
Efficient breaker systems which quickly and completely reduce the viscosity are in demand. Consequently, industry is constantly searching for improvements in breaker systems for thickened aqueous fluids.